diff --git a/plugins/check_disk.c b/plugins/check_disk.c
index 05e55022..6cb4cb2f 100644
--- a/plugins/check_disk.c
+++ b/plugins/check_disk.c
@@ -1027,7 +1027,7 @@ void
 print_usage (void)
 {
   printf ("%s\n", _("Usage:"));
-  printf (" %s {-w absolute_limit |-w  percentage_limit% | -W inode_percentage_limit } {-c absolute_limit|-c percentage_limit% | -K inode_percentage_limit } {-p path | -x device}\n", progname);
+  printf (" %s {-w absolute_limit |-w  percentage_limit%% | -W inode_percentage_limit } {-c absolute_limit|-c percentage_limit%% | -K inode_percentage_limit } {-p path | -x device}\n", progname);
   printf ("[-C] [-E] [-e] [-f] [-g group ] [-k] [-l] [-M] [-m] [-R path ] [-r path ]\n");
   printf ("[-t timeout] [-u unit] [-v] [-X type] [-N type]\n");
 }